EVALUATION AND RETROFITTING OF AN IRREGULAR SHAPED RC BUILDING

Abstract

Many existing buildings in India have shown distress and deterioration. The reinforcement corrosion and cracking are the common problems observed in RC buildings. But temperature distress is rarely reported in regular shaped building. Codes handle the problem of thermal stresses by providing movement/expansion joints at regular interval. But, in case of irregular shaped buildings, temperature movement can lead to severe distress and need to be investigated. A large number of buildings in India are irregular in terms of shape, stiffness, arrangement of structural elements, and mass. As per the IS 1893 (Part — I) — 2002, to perform well in an earthquake, a building should possess four main attributes, namely simple and regular configuration and adequate lateral strength, stiffness and ductility. IS code provisions are not applicable to irregular buildings. Therefore there is need to study the structural behavior of irregular shaped buildings in detail. Further, many buildings in India have been constructed in past, and are being constructed, even now, without giving proper attention to earthquake resistant design. Retrofitting is required to ensure safety of such buildings against gravitational as well as earthquake forces. An irregular shaped building of Wild Life Institute of India (WII), Dehradun has been considered for study in this dissertation. To match with the natural environment, the unique architectural design of WII building was selected through a National design competition in 1986. The shape of the buildings is inspired from the `Tent' structure. The height of the buildings varies from corners to the crown. The building has shown distress in the form of cracking of Beams, Columns, Joints and Masonry walls. Since the nature and location of distress in all the blocks is identical, it indicated a configurational/design deficiency. Therefore a detailed investigation of the building for the distress and safety against Gravity, Temperature and Earthquake loads has been done. The building is highly asymmetric in plan and irregular in elevation, and therefore, a three dimensional analytical model for the building has been developed in SAP 2000 Nonlinear software for simulation of behavior under Gravity, Temperature and Earthquake loading. Investigation for these actions has been carried out, as per relevant IS codes. Building has been found to be inadequate against the current codal provisions iii for gravity and temperature loads, in linear static analysis. In nonlinear analysis building has been found to be safe against gravity loading, and it explains how the building is standing, although being deficient as per code. But under temperature load, the short columns and masonry walls in the building, fail in shear, while, the long columns are safe which is in agreement with the real situation. The primary cause of distress in the buildings has been identified to be the temperature movement, as the building has long monolithic corridors and peculiar structural shape. Accordingly, alternative measures have been suggested for repairing of distressed components, relieving the temperature stresses, and retrofit of short anchor columns.